JP6415540B2 - Carbon nanomaterial coating method - Google Patents

Description

Field of Invention

  The present invention relates to carbon-based nanomaterials, and in particular to coating such materials.

  Carbon-based nanomaterials (CNM) have recently received much attention due to their excellent mechanical and electrical properties. For example, carbon nanotubes (CNT), carbon nanofibers (CNF) and graphene, due to their superior mechanical characteristics, including high tensile strength and high modulus, and high thermal and high electrical conductivity, It is an ideal raw material for various applications.

  Therefore, research for actual application of CNM has been actively promoted. In particular, metal composites containing these nanomaterials are promising as new materials that provide improved and unique functionality. For example, metal-CNF composites are expected to have high strength and high thermal conductivity. However, due to the poor wettability of CNF with molten metals such as tin alloys, aluminum and silver, some defects and vacancies may be detected in the composite, which can be found in all types of CNMs. It is a common problem that exists. Therefore, it is necessary to modify the surface of the CNM before combining with the metal alloy.

  Applying a metal coating to the surface is one of the most effective ways to improve the wettability of those molten metals. Metallization or deposition can also impart various beneficial properties to the CNM, such as high average density, good solubility in various solvents, and desirable magnetic and catalytic properties. Metal-coated CNMs are not removed as impurities by solder flux after reflow due to their high average density. A homogeneous metal coating layer can also act as a barrier to prevent nanomaterial aggregation, thereby facilitating obtaining a well-dispersed CNM suspension. A ferromagnetic metal coated CNM can be controlled by a magnetic field, which may result in a CNM composite having a highly controlled microtexture. A CNM deposited with catalytic metal particles may provide an excellent catalyst for applications such as improved fuel cell electrodes.

  Thus, a uniformly dispersed metal coating on the surface of the CNM becomes critical to achieving the interesting properties described above. However, the inert nature of CNM also leads to weak interaction with the surroundings and is therefore a challenge in terms of surface functionalization (including uniform deposition of metal nanoparticles). Although metallic coating methods for CNM are known, conventional sensitizing methods such as simply pretreating CNM using tin (II) ions as the sensitizer are not very successful due to the strong surface inertness of CNM. However, the conventional nitric acid treatment cannot precisely control the reaction between carbon and nitric acid, so that a sufficient activation point cannot be formed. All of these factors will have a negative effect on the particle size distribution and uniformity of the deposited metal nanoparticles.

  In view of the above desired properties of coated nanomaterials and the above and other shortcomings of the prior art, it is an object of the present invention to provide an improved method of autocatalytic plating of carbon nanomaterials.

  Therefore, according to the first aspect of the present invention, a method for autocatalytic plating of carbon nanomaterials is provided, the method comprising preparing a carbon nanomaterial in an oxidizing solution containing at least two oxidizing agents, Maintaining within the first temperature range and stirring the solution for a first predetermined time; heating the solution to reach a second temperature range higher than the first temperature range; Stirring the solution for a second predetermined time shorter than the first time, maintaining the temperature range, removing the nanomaterial from the oxidizing solution, and adding the nanomaterial to the sensitized aqueous solution containing the sensitizer. Dispersing the nanomaterial from the sensitizing solution; immersing the nanomaterial in a seed mixture including seed particles attached to the nanomaterial; removing the nanomaterial from the seed mixture; Contains a metal source and a first aqueous reducing agent Immersing the nanomaterial in the plating solution, plating the nanomaterial such that the metallic layer grows from the seed particles onto the nanomaterial, removing the nanomaterial from the plating solution, and a second reducing agent. A step of dispersing the nanomaterial in the aqueous solution, and heating the solution to reach the third temperature range and maintaining the solution in the third temperature range while subjecting the heated solution to ultrasonic treatment. Performing for a predetermined time.

  Carbon nanomaterial (CNM) is to be understood within this context as a carbon-based material or structure having at least some characteristics in the nanometer particle size range.

  Autocatalytic plating, sometimes referred to as electroless plating or chemical plating, relates to a method in which the reaction is carried out in an aqueous solution without the use of external power.

  The step of removing the carbon nanomaterial from the respective solutions and / or mixtures may be performed by any conventional method known to those skilled in the art, for example, filtration and / or drying.

  In the present invention, by using at least two different oxidants (plural oxidants) in the pretreatment step, the surface of the CNM is oxidized by a plurality of oxidants that strongly affect carbon in a certain temperature range. Is based on the recognition. Thereby, the degree of oxidation can be precisely controlled by modifying the reaction temperature and reaction time. Controlling the degree of oxidation of the CNM is extremely important because if the degree of oxidation is too high, the structure of the carbon material may be destroyed.

Here, the oxidation is divided into two steps, and a low temperature is maintained for a long time at the beginning of the method to allow the oxidant to penetrate into the spacing of the carbon molecules. The temperature is then raised and maintained for a shorter time to cause the reaction. In this process, the original stable sp ² carbon-carbon bond was suddenly broken, and instead sufficient reversible oxygen-containing groups were formed on the surface of the CNM without destroying the entire structure of the material. The temperature may be increased rapidly.

  After performing surface oxidation, the dispersion, particle size and geometry of the metal nanoparticles on the surface of the CNM are well controlled as a result of the presence of the complexing agent and the special properties of the reducing agent to provide a dense and homogeneous surface on the substrate surface. A metallic layer was synthesized by an electroless deposition method capable of depositing metal nanoparticles. Thereafter, reduction of the metal-coated CNM can remove most of the oxygen-containing groups from the carbon surface and reform the carbon-carbon bond.

  In one aspect of the invention, the first temperature range may advantageously be −10 to 10 ° C. and the first time may be 1 hour to 8 hours.

  In one aspect of the invention, the second temperature range may advantageously be 30-50 ° C. and the second time may be 10-60 minutes. It has been found that in the above temperature range and time, efficient oxidation of CNM is possible without destroying the original structure of CNM.

  According to one aspect of the invention, the oxidizing agent may advantageously comprise at least two of sulfuric acid, nitric acid, potassium permanganate, potassium dichromate and sodium nitride. For example, by using sulfuric acid molecules, penetrating through various layers of CNTs, carrying potassium permanganate molecules inward, and realizing oxidation, thereby forming a sufficient amount of oxidation spots, followed by a metal coating method Can be made easier.

  Furthermore, the sensitizer may preferably comprise formaldehyde, polyvinylpyrrolidone or tin (II) chloride.

  In one aspect of the invention, the step of removing the nanomaterial from the oxidizing solution may advantageously comprise filtering the nanomaterial and rinsing with deionized water until the pH value of the rinse liquid is about 7. Good. Thereby, by monitoring the pH value, it can be determined that all of the oxidant has been removed and that only the carbon nanomaterial remains.

  According to one aspect of the invention, the seed particles may advantageously contain palladium. Palladium may be supplied from, for example, palladium chloride. However, other metals such as gold silver and copper may be used as seed particles.

  According to one aspect of the present invention, the first reducing agent may include cobalt sulfate, ferrous chloride, formaldehyde, polyvinylpyrrolidone, aqueous ammonia, ethylenediamine, ethylenediaminetetraacetic acid, or benzotriazole.

  According to one aspect of the invention, the step of plating may advantageously include removing dissolved oxygen in the solution with ultrasound to avoid oxidation of the reducing agent.

  According to one aspect of the present invention, the plating step may be performed in a closed container while passing nitrogen gas through the solution.

  According to one aspect of the invention, the aqueous metal source may comprise palladium, silver, gold or nickel.

  In one embodiment of the present invention, the aqueous metal source may be a metal ion source selected from the group comprising silver nitride, palladium chlorate, gold chloride, nickel chloride, aqueous ammonia, ammonium sulfate, ethylenediamine and ethylenediaminetetraacetic acid. Good.

  In one embodiment of the present invention, the third temperature range may be 60-100 ° C. and the third time may be at least 1 hour.

  In one embodiment of the present invention, the carbon nanomaterial may be a carbon nanotube, a carbon nanofiber, or graphene. Of course, other similar carbon-based nanomaterials can be used. Furthermore, similar carbon nanomaterials may be referred to by different names, such as nanorods, nanopillars, nanowires, and the like.

  In one embodiment of the present invention, the plating step may be performed for 0.5 to 24 hours. The plating time determines the thickness of the metallic coating obtained on the CNM. Therefore, it is possible to achieve a desired coating thickness by controlling the plating time.

  According to one aspect of the present invention, the second reducing agent may advantageously be selected from the group comprising potassium hydroxide, sodium borohydride, pyrogallol, L-ascorbic acid and hydrazine monohydrate. Good. The second reducing agent is preferably a strong reducing agent.

  Other features and advantages of the present invention will become apparent from a detailed study of the appended claims and the following description. Those skilled in the art will appreciate that different features of the present invention may be combined to create embodiments other than those described below without departing from the scope of the present invention.

  These and other aspects of the invention will now be described in more detail with reference to the accompanying drawings, which illustrate exemplary embodiments of the invention.

FIG. 1 is a flowchart outlining the general steps of a method according to one aspect of the present invention. FIG. 2a is a TEM image showing a material made according to one aspect of the present invention. FIG. 2b is a TEM image showing a material made according to one aspect of the present invention. FIG. 3a is a TEM image showing a material made according to one aspect of the present invention. FIG. 3b is a TEM image showing a material made according to one aspect of the present invention. FIG. 4 is an XRD diffraction pattern of a material coated according to one embodiment of the present invention.

Detailed Description of the Preferred Embodiments of the Invention

  In this detailed description, various aspects of the coating method of nanomaterials according to the present invention will be mainly described with reference to carbon nanomaterials (CNM) such as carbon nanotubes, carbon nanofibers or graphene (hereinafter referred to as CNM).

  A method of manufacturing a coated nanomaterial will be described with reference to the flow diagram of FIG. 1 that outlines the general steps of the method.

  Initially (102), the selected CNM is rinsed with acetone and deionized water to remove any impurities and protective layers from the surface of the CNM.

  After rinsing, the CNM is mixed with a plurality of oxidants at a temperature in the range of about −10 to 10 ° C. (104), followed by stirring at that temperature for 1 to 4 hours without causing strong oxidation to occur. To enter the surface of the CNM.

  The oxidizing agent includes at least two of sulfuric acid, nitric acid, potassium permanganate, potassium dichromate, and sodium nitride. Sulfuric acid and sodium nitride act as an intercalating agent to carry the oxidizing agent to the inner layer of the CNT, and an oxidizing agent, which may be potassium permanganate, performs surface oxidation of the CNT. In order to avoid explosive reactions, the oxidant should be added to the sulfuric acid very slowly.

  Next, in order to maintain in the range of 30-50 degreeC, stirring for about 0.5 hour-3 hours, temperature is raised and controlled.

  The oxidized CNM is then separated from the solution by using vacuum filtration, and then the CNM is washed several times with deionized water until the pH of the filtrate is about 7 to remove the oxidant completely. To be sure.

  After washing, the oxidized CNM is dispersed in the aqueous sensitizer solution, thus sensitizing the CNM (106). The sensitizer may be selected to be, for example, formaldehyde, polyvinyl pyrrolidone or tin (II) chloride.

  After sensitization, CNM is immersed in a solution containing palladium chloride and activated by palladium particles adhering to CNM (108), then centrifuged and distilled until the pH of the filtered solution is 7.0. Rinse with water. The CNM coated with the palladium species is then recovered and dried in a vacuum oven. Palladium seed particles are particularly advantageous as a nucleation point for subsequent silver growth because palladium is an excellent catalyst for triggering the silver self-plating process.

  Next, the activated CNM is immersed in the autocatalytic plating solution. The autocatalytic plating solution is prepared as two separate solutions, an aqueous metal ion source solution and an aqueous reducing agent solution, with equal amounts mixed prior to plating. Plating (110) is performed at room temperature and the deposition time depends on the required coating thickness. For example, the growth rate of metal nanoparticles on the CNM may be about 0.5 nm / hour. In order to avoid oxidation of the reducing agent, the dissolved oxygen in the deionized water is ultrasonically removed, and the deposition is performed in a closed container while passing nitrogen gas through the solution. Thereby, a carbon-based nanomaterial having a uniform metal coating with a clear outline is provided without damaging the structure of the carbon nanomaterial.

  The cobalt reducing agent aqueous solution may be one or more of the following chemical substances: cobalt sulfate, ferrous chloride, formaldehyde, polyvinylpyrrolidone, aqueous ammonia, ethylenediamine, ethylenediaminetetraacetic acid, and benzotriazole.

  The aqueous metal ion source solution can be one or more of silver nitride, palladium chlorate, gold chloride, nickel chloride, aqueous ammonia, ammonium sulfate, ethylenediamine and ethylenediaminetetraacetic acid. Thereby it may be coated with a metal such as palladium, silver, gold and nickel. Typically, it may be desirable to provide a metal coating having a thickness in the range of 5-100 nm.

  After the reaction is complete, i.e., the desired thickness has been reached, the metal coated CNM is filtered and washed until the color of the filtrate is substantially clear. After washing, sonication is used to redisperse the CNM in deionized water with a strong reducing agent (112). A second reducing solution is used to remove oxygen-containing groups on the CNM. The second reducing solution can be one or more of the following chemicals. Potassium hydroxide, sodium borohydride, pyrogallol, L-ascorbic acid and hydrazine monohydrate. The reduction method is carried out at 60 to 100 ° C. for several hours, for example, 1 to 12 hours. Finally, the metal coated CNM is filtered off and dried in a vacuum oven until no mass loss is observed.

  The morphology of the CNM coated with the silver layer was examined with a transmission electron microscope (TEM). The elemental composition and structural analysis of the sample were analyzed by X-ray diffraction (XRD).

  FIG. 2a shows a TEM image of the initial carbon nanofiber (CNF), and FIG. 2b is an image of the carbon nanofiber coated with silver nanoparticles. A CNF with a diameter of 50 nm was selected to demonstrate the coating method. After coating, a layer of 3-5 nm diameter silver nanoparticles was uniformly dispersed on the CNF surface without destroying its original structure.

  3a-b are TEM images showing silver-coated graphene at different magnifications. After coating, a layer of silver nanoparticles with a controlled particle size of 2-3 nm was uniformly dispersed on both sides of the graphene sheet to form a silver / graphene / silver hybrid material. Since the silver coating layer was thin, it did not affect the graphene properties.

  FIG. 4 shows an X-ray diffraction (XRD) diffraction pattern of a silver-coated carbon nanofiber sample. In the diffraction pattern, the presence of silver is confirmed by the appearance of peaks corresponding to the face-centered cubic (FCC) structure of metallic silver, most notably the appearance of (111) reflection.

  Although the present invention has been described with respect to specific exemplary embodiments thereof, many different changes, modifications, etc. will become apparent to those skilled in the art.

  Further, by studying the drawings, disclosure, and appended claims in detail, those skilled in the art can appreciate and achieve modifications to the disclosed embodiments in carrying out the claimed invention. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality.

Claims (12)

A method for autocatalytic plating of carbon nanomaterials, the method comprising preparing a carbon nanomaterial in an oxidizing solution containing at least two oxidizing agents, and maintaining the oxidizing solution within a first temperature range; Stirring the oxidizing solution for a first predetermined time;
The oxidizing solution is heated to reach a second temperature range higher than the first temperature range, and the oxidizing solution is kept in the second temperature range while maintaining the oxidizing solution within the second temperature range. Stirring for a second predetermined time shorter than one time;
Removing the nanomaterial from the oxidizing solution;
Dispersing the nanomaterial in a sensitized aqueous solution containing a sensitizer comprising formaldehyde, polyvinylpyrrolidone or tin (II) chloride ;
Removing the nanomaterial from the sensitizing solution;
Immersing the nanomaterial in a solution containing palladium to attach palladium seed particles to the nanomaterial ; and
Removing the nanomaterial from the palladium-containing solution ;
Plating the nanomaterial such that a metallic layer is grown from the palladium seed particles on the nanomaterial by immersing the nanomaterial in a plating solution comprising an aqueous metal source and a first aqueous reducing agent. When,
Removing the nanomaterial from the plating solution;
Dispersing the nanomaterial in an aqueous solution containing a second reducing agent;
By heating water solution containing the second reducing agent, to reach a third temperature range, while maintaining a water solution containing the second reducing agent in the third temperature range, heated pressurized look including a step of reducing the second reducing agent by ultrasonic treatment of water solution containing the second reducing agent third predetermined time,
The oxidizing agent comprises potassium permanganate and sulfuric acid;
The first temperature range is −10 to 10 ° C., the first time is 1 hour to 8 hours,
The method wherein the second temperature range is 30 to 50 ° C. and the second time is 10 to 60 minutes . The oxidizing agent further comprises at least one of potassium dichromate and sodium nitride The method according to 請 Motomeko 1. Wherein the step of extracting the nanomaterial from the oxidizing solution, the nano material was filtered until the pH value of the rinsing solution is about 7 comprises rinsing with deionized water, according to 請 Motomeko 1 or 2 Method. It said first reducing agent is cobalt sulfate, ferrous chloride, formaldehyde, polyvinyl pyrrolidone, aqueous ammonia, ethylenediamine, ethylenediaminetetraacetic acid or benzotriazole The method of any one of 請 Motomeko 1-3 . Wherein the step of plating, the dissolved oxygen of the plating solution was removed by ultrasonic, thus including avoiding oxidation of the reducing agent, the method according to any one of 請 Motomeko 1-4. Process, the plating solution is performed in a nitrogen, while passing the gas closed container during method according to any one of 請 Motomeko 1-5 to the plating. Metal source of the aqueous, palladium, silver, including gold or nickel, the method according to any one of 請 Motomeko 1-6. Metal source of the aqueous silver nitride, chlorate palladium, a metal ion source selected from the group comprising gold chloride and nickel chloride method according to any one of 請 Motomeko 1-7. The third temperature range is 60 to 100 [° C., the third time, at least 1 hour A method according to any one of 請 Motomeko 1-8. The carbon nanomaterials, carbon nanotubes, carbon nanofibers, or graphene method according to any one of 請 Motomeko 1-9. Step is carried out for 0.5 hours to 24 hours, A method according to any one of 請 Motomeko 1 to 10 wherein the plating. The second reducing agent, potassium hydroxide, sodium borohydride, pyrogallol, is selected from the group comprising L- ascorbic acid and hydrazine monohydrate, according to any one of 請 Motomeko 1-11 the method of.